﻿294 DR. A. VAUGHAN ON THE PAL2EONTOLOGICAL [May I905, 



than connote certain characters which are common to a great 

 number of Ckonetes, without implying genetic relationship. In 

 addition to the generic characters, Chonetes cf. Inardrensis implies 

 small size, slight convexity, and the increase of ribs by forking and 

 intercalation. On the other hand, Ch. layuessiana, de Kon., can 

 only be correctly applied to a particular group of the hardrensis- 

 circulus, which is characterized by a strongly-transverse shell and 

 very fine ribbing. 



The distinction of the forms which occur at different horizons 

 must necessarily depend upon very small differences, but will 

 probably be possible when a very large number of specimens have 

 been collected from each horizon. At present, I am unable to 

 separate definitely from certain Tournaisian forms the specimens 

 which occur in D 2 and e in the Bristol and surrounding areas. 



On the other hand, certain varieties apparently characterize par- 

 ticular zones throughout the Bristol and surrounding areas. For 

 example, a characteristic form (Chonetes cf. laguessiana) of the 

 Lower Tournaisian (K and ZJ has a flattened, strongly-transverse, 

 rectangular shell and very fine, close striae. Compare Davidson, 

 'Monogr. Brit. Foss. Brachiop.' vol. ii (1858-63) pi. xlvii, fig. 19 ; 

 but usually the form is nearly as large as fig. 19 b. 



Davidson, op. cit. pi. xlvii, fig. 13, gives the form, and in fig. 12 c 

 the manner of ribbing, characteristic of that mutation which is 

 abundant at the top of the Tournaisian (C) ; in this form the 

 shell is nearly semicircular, and moderately convex. 



Chonetes cf. crassistria (M'Coy) and Chonetes ' Buchiana,' Dav. 

 (? de Kon.), Davidson, ' Monogr. Brit. Foss. Brachiop.' vol. ii 

 (1858-63) pi. xlvii, figs. 17, 28 & pi. lv, fig. 12. 



I am far from satisfied that the shell, which is so characteristic 

 of K x in the Bristol area, has been correctly referred to Chonetes 

 Buchiana, de Kon., by Davidson. The concentric, erect lamination, 

 so characteristic of the Bristol form, appears to be entirely absent 

 from the type of de Koninck's species. 



Chonetes cf. crassistria is employed in the text, to cover small 

 Chonetes with coarse ribbing which forks on the hardrensis-jAsni. 

 There is a complete transition between these forms and Chonetes 

 ' Buchiana ', Dav. The ribs in a typical example of Chonetes cf. 

 crassistria often exhibit the transverse, erect scales which charac- 

 terize Ch. cf. Buchiana ; and, by a diminution in forking, Ch. cf . 

 crassistria passes imperceptibly into Ch. cf. Buchiana. 



Chonetes papilionacea, Phil., and Chonetes cf. comoides (J. Sow ). 

 (PI. XXYI, fig. 3.) 



Compare Davidson, ' Monogr. Brit. Foss. Brachiop.' vol. ii (1858-63) pi. xlvi, 

 figs. 3-5. 



Chonetes papilionacea denotes finely-ribbed, flattened forms, with 

 a thin shell. The pits in the under layer of the test are 

 small, circular, and adjacent. 



